1. Field of the Invention
This invention relates to a data transfer method, an image processing method, a data transfer system and an image processor for transferring digital data, especially image data.
2. Description of the Related Art
For instance, there is a case that image data, which is prepared by the image preparing means such as the scanner (the handy scanner, in particular), the digital camera and etc., are stored temporarily in a hard disk of the personal computer through a specific transmission channel (the bus) and then devoted to the printing or displaying.
In such case, if the capability of the data processing in the bus or the device at transfer end falls short of the transfer size, the image data is compressed in size corresponding to the capability of the bus or the device at transfer end and then transferred to the device.
Here explains about a conventional method capable of setting flexibly the relation between the picture quality and the compression ratio, it has been well known the method (Japanese laid-open publication No. 09-083809) of handling a block size (which will be described later) and the number of colors as a parameter. The processing method is explained according to FIG. 13.
In this method, the image data is divided into blocks including a plurality of pixels. The block is to be represented approximately by a specific number of colors. Accordingly, it is possible to change the compression ratio by changing the number of pixels (a block size) included in the block or by changing the number of colors.
In FIG. 13, in case of changing the block size and the number of approximate colors to be set by parameter setting means 91, the compression ratio determined uniquely by those parameters is set in compressing means 94. The compressing means 94 can determine the compression ratio so as to meet with the memory size of storage means 95. According to such configuration, the compressing means 94 extracts the approximate colors from each block prepared by input means 92 and then stores them per block in the storage means 95.
In the conventional image processing method described above, the compression ratio is arranged to be set based on the matching of the memory size in such way. In order to obtain a desired picture quality and the compression ratio, the block size and the number of approximate colors are set as parameters.
On the other hand, considering the case of transferring the data from a specific device to the other specific device (for example, in case where a handy scanner is connected with a personal computer and the data is transferred from the handy scanner to the personal computer), and the handy scanner has to be provided with a memory equipped with a buffer function. However, from the aspects of the measurement and the price, the handy scanner cannot be provided with a mass memory including the buffer function. Therefore, if the transfer rate cannot be ensured sufficiently, the buffer will be overflowed and the lack of data will occurs. Therefore, the compression ratio must be determined corresponding to the data transfer rate between devices.
In addition, the device for reading the original surface operating the image sensor manually, like the handy scanner, repeats the stop and acceleration of the scanning so that the data size to be transferred can be adjusted, thereby it is possible to prevent the lack of data that appears because the buffer memory is small in size. However, under such method, since the position of image to be read various widely and the reading speed is not stable, the picture quality deteriorates. And the great difference of the picture quality is caused by the insufficiency of the user's skill causes. In such case, though the operation speed can be adjusted by increasing the size of buffer memory, a problem of the cost-up still remains.